1. Technical Field
The present invention relates generally to wheel profile measurement, and more specifically, to a method, apparatus, and system for non-contact profile measurement of a train wheel.
2. Description of Related Art
Manual wheel measurement is a well established practice in the railway industry. Over a period of use, a train wheel will experience wear and possibly damage. The metallic structure of train wheels is designed to allow for slow deformation caused by wear or damage over a period of time, thereby reducing the possibility of complete structural failure. To monitor this deformation, the profile of the train wheel is constantly monitored.
Although in certain circumstances a railway wheel profile can be measured while a train is in motion, wheel profiles are also measured in the field or in a repair shop while the train has stopped or while the railway wheel is uninstalled. Proper maintenance, cost savings and derailment prevention are major goals of wheel profile measurement. There are two ways in which the above goals can be accomplished while the train is stopped or while the wheel is uninstalled, contact measurement and non-contact measurement.
Contact measurement means include measuring devices that, when taking measurements, the measuring device must physically touch the railway wheel at the point of measurement. These means include, among others, caliper-based, gauge-based and roller-based measurement devices. Contact means has certain disadvantages and limitations, though. Contact measurement devices are typically inaccurate and difficult to use because of the various points of measurement required to obtain a wheel profile.
Non-contact wheel profile measurement devices include magnetic, eddy current, and laser (or light) measurement methods. Current art magnetic and eddy current measurement methods are limited in that structure differences from wheel to wheel, either through latent defects or defects caused while the railway wheel is in operation, may cause erroneous or inaccurate readings.
Current art non-contact measurement means that use light carry certain limitations as well. For instance, in order to measure multiple wheel data points to construct a profile, current art methods typically require multiple sensors and/or multiple light emitters to measure reflected light. Because of the number of sensors used, these apparatuses are typically bulky, difficult to align, difficult to use, and have power requirements that reduce the usefulness as a hand-held device, if embodied in that manner.
Additionally, current art methods cannot measure certain measurement points that are beyond the visible and measurable viewing area of the lasers and their sensors. As an example, a witness groove of a railway wheel, which is typically located on the outside surface of the railway wheel, is measured to determine the wear on the railway wheel.
Because of its location, on a side of the wheel, the witness groove is not visible or measurable from current art non-contact measurement devices. Further, because the calculation of the wheel diameter uses the witness groove measurement, current art methods are limited in their ability to provide a wheel diameter measurement as well.
Furthermore, because of the multiple lasers and sensors used by current art non-contact measurement devices, a number of points of contact are required to properly locate the device to take accurate measurements. Some devices, in order to obviate the difficulty in placement of the device in a calibrated location, require additional sensors and placement detectors that assist the user in determining when the device is in a calibrated position. This limitation not only increases the complexity of the device, but causes time delays in measuring railway wheels as the user must intricately position the device prior to measurement.
Additionally, because current art non-contact measurement devices are typically a static size that fits over the railway wheel, current are devices do not provide for variability of wheel size. Deviations, whether slight or significant, from a standard railway wheel size may cause measurement errors because of the static size of the measurement device. Significant deviations may cause the device not to be able to fit onto a railway wheel. As such, current art non-contact measurement devices are limited in the size and shape of a railway wheel that the devices may be used on.
Finally, witness groove diameters may vary from manufacturer to manufacturer. Because of the limited variability of current art non-contact measurement devices, the inability to measure the witness groove to determine wheel diameter, and thus wear, further limits the capabilities of the current art.
What is needed is a system, method and apparatus that overcomes the limitations of the prior art, namely, accuracy, portability, ease of use, and provides the user with an ability to measure the witness groove and wheel diameter as well as other measurement points.